(a) Field of the Invention
The present invention relates to an organic compound and an organic photoelectric device including the same. More particularly, the present invention relates to an organic compound that easily dissolves in an organic solvent, and is applicable as a host material of an emission layer of an organic photoelectric device since it emits fluorescence and phosphorescence at a red wavelength through a blue wavelength, and an organic photoelectric device including the same.
(b) Description of the Related Art
An organic photoelectric device includes an organic light emitting material between a rear plate including ITO transparent electrode patterns as an anode on a transparent glass substrate and an upper plate including a metal electrode as a cathode on a substrate. When a predetermined voltage is applied between the transparent electrode and metal electrode, current flows through the organic light emitting material to emit light.
Such an organic light emitting material for an organic photoelectric device was firstly developed by Eastman Kodak, Inc., in 1987. The material is a low molecular aromatic diamine and aluminum complex as an emission-layer-forming material (Applied Physics Letters. 51, 913, 1987). C. W Tang et al. firstly disclosed a practicable device as an organic photoelectric device in 1987 (Applied Physics Letters, 51 12, 913-915, 1987).
According to the reference, the organic layer has a structure in which a thin film (hole transport layer (HTL)) of a diamine derivative and a thin film of tris(8-hydroxy-quinolate)aluminum (Alq3) are laminated. The Alq3 thin film functions as an emission layer for transporting electrons. The Alq3 thin film functions as an emission layer for transporting electrons.
Generally, the organic photoelectric device is composed of an anode of a transparent electrode, an organic thin layer of a light emitting region, and a metal electrode (cathode) formed on a glass substrate, in that order. The organic thin layer may includes an emission layer, a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), or an electron injection layer (EIL). It may further include an electron blocking layer or a hole blocking layer due to the emission characteristics of the emission layer.
When the organic photoelectric device is applied with an electric field, holes and electrons are injected from the anode and the cathode, respectively. The injected holes and electrons are recombined on the emission layer though the hole transport layer (HTL) and the electron transport layer (ETL) to provide light emitting excitons.
The provided light emitting excitons emit light by transiting to the ground state.
The light emitting may be classified as a fluorescent material including singlet excitons and a phosphorescent material including triplet excitons.
Recently, it has become known that the phosphorescent light emitting material can be used for a light emitting material in addition to the fluorescent light emitting material (D. F. O'Brien et al., Applied Physics Letters, 74 3, 442-444, 1999; M. A. Baldo et al., Applied Physics letters, 75 1, 4-6, 1999). Such phosphorescent emission occurs by transiting electrons from the ground state to the exited state, non-radiative transiting of a singlet exciton to a triplet exciton through intersystem crossing, and transiting the triplet exciton to the ground state to emit light.
When the triplet exciton is transited, it cannot directly transit to the ground state. Therefore, the electron spin is flipped, and then it is transited to the ground state so that it provides a characteristic of extending the lifetime (emission duration) to more than that of fluorescent.
In other words, the duration of fluorescent emission is extremely short at several nanoseconds, but the duration of phosphorescent emission is relatively long such as at several microseconds, so that it provides a characteristic of extending the lifetime (emission duration) to more than that of the fluorescent emission.
In addition, evaluating quantum mechanically, when holes injected from the anode are recombined with electrons injected from the cathode to provide light emitting excitons, the singlet and the triplet are produced in a ratio of 1:3, in which the triplet light emitting excitons are produced at three times the amount of the singlet light emitting excitons in the organic photoelectric device.
Accordingly, the percentage of the singlet exited state is 25% (the triplet is 75%) in the case of a fluorescent material, so it has limits in luminous efficiency. On the other hand, in the case of a phosphorescent material, it can utilize 75% of the triplet exited state and 25% of the singlet exited state, so theoretically the internal quantum efficiency can reach up to 100%. When a phosphorescent light emitting material is used, it has advantages in an increase in luminous efficiency of around four times that of the fluorescent light emitting material.
In the above-mentioned organic light emitting diode, a light emitting colorant (dopant) may be added in an emission layer (host) in order to increase the efficiency and stability in the emission state.
In this structure, the efficiency and properties of the light emission diodes are dependent on the host material in the emission layer. According to studies regarding the emission layer (host), the organic host material can be exemplified by a material including naphthalene, anthracene, phenanthrene, tetracene, pyrene, benzopyrene, chrysene, pycene, carbazole, fluorene, biphenyl, terphenyl, triphenylene oxide, dihalobiphenyl, trans-stilbene, and 1,4-diphenylbutadiene.
Generally, the host material includes 4,4-N,N-dicarbazolebiphenyl (CBP) having a glass transition temperature of 110° C. or less and a thermal decomposition temperature of 400° C. or less, in which the thermal stability is low and the symmetry is excessively high. Thereby, it tends to crystallize and cause problems such as a short and a pixel defect according to results of thermal resistance tests of the devices.
In addition, most host materials including CBP are materials in which the hole transporting property is greater than the electron transporting property. In other words, as the injected hole transportation is faster than the injected electron transportation, the excitons are ineffectively formed in the emission layer. Therefore, the resultant device has deteriorated luminous efficiency.
Accordingly, in order to realize a highly efficient and long lifetime organic light emitting device, it is required to develop a phosphorescent host material having high electrical and thermal stability and that is capable of transporting both holes and electrons.